Field of the Invention
The present invention relates to a die cushion-cum-slide cushion device and a method of controlling the same, and more particularly to a technique of allowing a servo motor used for the die cushion device to be also used for the slide cushion device.
Description of the Related Art
Heretofore, a servo die cushion device using a servo motor has been described in Patent Literature 1 (Japanese Patent Application Laid-Open No. JP 2006-315074 A) and Patent Literature 2 (International Publication No, WO 2010/058710 A1).
The die cushion device described in Patent Literature 1 is configured to allow a lower chamber (pressure generating chamber) of a hydraulic cylinder supporting a cushion pad to be directly connected to a discharge port of a hydraulic pump/motor so that torque of a servo motor connected to a rotating shaft of the hydraulic pump/motor is controlled to enable pressure (die cushion force) in the lower chamber of the hydraulic cylinder to be controlled.
The die cushion device described in Patent Literature 1 requires a servo motor of large capacity that can supply all power required for die cushioning simultaneously with the die cushioning. If a servo motor increases in capacity, a die cushion device increases in size, as well as power-receiving equipment increases in capacity.
The die cushion device described in Patent Literature 2 is configured to allow a proportional valve and a hydraulic pump/motor to be connected in parallel with a lower chamber of a hydraulic cylinder to reduce capacity of a servo motor for driving the hydraulic pump/motor so that opening of the proportional valve and torque of the servo motor are controlled when die cushion force is controlled.